1. Field of the Invention
The present invention relates to a rotation angle detection apparatus having a non-contact sensor that detects the rotation angle of a rotating member by detecting a change in the azimuth of magnetic flux.
2. Description of the Related Art
In the past, as a rotation angle detection apparatus for detecting the rotational angle of a throttle valve, there has been known one which includes a gear wheel that is formed by insert molding a metal plate made of a cup-shaped non-magnetic material into the interior thereof, a permanent magnet and a yoke that are fitted into a notched portion formed in a central portion of the gear wheel, and a non-contact sensor that is fixedly secured to a non-rotating member, wherein the rotation angle of the rotating member is detected by detecting a change in the azimuth of the magnetic flux lines of the permanent magnet that is rotating together with the rotation of the gear wheel by means of the non-contact sensor (see, for example, a first patent document: Japanese patent application laid-open No. 2005-233768 (Paragraph No. 0019, FIG. 13)).
However, with the above-mentioned rotation angle detection apparatus, the end faces of the permanent magnet and the yoke are in abutment with the metal plate, so there is the following problem. That is, an eddy current, which is generated in the body of the detection apparatus under the action of electromagnetic waves from the outside, and/or radio wave noise from a drive motor are transmitted to the yoke and the permanent magnet through a throttle shaft and the metal plate, from where they are propagated through radiation to the non-contact sensor as it is, thus resulting in a factor for malfunction of the non-contact sensor.